1. Field of the Invention
The present invention relates to a thin-film magnetic head, a head gimbal assembly, and a hard disk drive which read magnetic information of a hard disk or the like by utilizing a magnetoresistive effect.
2. Related Background Art
As a thin-film magnetic head for reading magnetic information of a hard disk, MR (MagenetoResistive) heads have been in use. The MR heads utilize a magnetoresistive effect in which the ohmic value of a magnetic body varies as an external magnetic field (e.g., a leakage magnetic field from the hard disk) changes when a current is caused to flow through the magnetic body. This magnetoresistive effect can substantially be realized by an MR film comprising a pinned layer whose direction of magnetization is fixed by exchange coupling with an antiferromagnetic layer, a free layer whose direction of magnetization varies depending on the external magnetic field, an intermediate layer disposed therebetween, and the like which are laminated. In a GMR (Giant MagnetoResistive) head utilizing a giant magnetoresistive effect, the intermediate layer is formed from an electrically conductive material such as Cu.
A constant sense current is supplied to the MR film of a magnetic head. As the angle between directions of magnetization of pinned layer and free layer is changed by the external magnetic field, the resistance to the sense current is minimized when the respective directions of magnetization of these layers coincide with each other and is maximized when their directions of magnetization are opposite from each other. Reading such a change in resistance as a voltage value can produce the magnetic information written in a hard disk.
Developed in the thin-film magnetic heads are the CIP (Current In Plane) structure in which the sense current flows in the surface direction of the MR film and the CPP (Current Perpendicular to Plane) structure in which the sense current flows in a direction (film thickness direction) perpendicular to the MR film. The CPP structure can use a magnetic shield layer itself as an electrode, thereby yielding no substantial short circuit (insulation failure) between the magnetic shield layer and the MR film, which may become a problem when narrowing the lead gap in the CIP structure. Therefore, the CPP structure is quite advantageous in enhancing the areal density of hard disks. Examples of heads employing the CPP structure include TMR (Tunneling MagnetoResistive) heads utilizing a magnetoresistive effect occurring at a tunnel junction and CPP-GMR heads (disclosed in Japanese Patent Application Laid-Open No. 2001-203408, for example).